Tom Glasgow: Red maple: Native in a strange land

Landscape red maples should be planted into native, pre-existing soils that have not been compacted or otherwise altered by development and construction activities. Try to avoid dry, sandy soils and all day full sun.

Tom Glasgow/Contributed photo

Published: Friday, June 14, 2013 at 04:57 PM.

Lately I seem to be running into quite a number of samples, phone calls and emails regarding red maples with dieback in the canopy and a dark, bumpy material on the branches and twigs.

Red maple (Acer rubrum) is native to Craven County and is quite abundant in and around our wetlands, along streams, and in low-lying areas that tend to stay moist. But red maple doesn’t appear to be particularly adaptable to the non-native stresses and challenges found in parking lots, along streets, and in many home landscapes.

The dark, bumpy discoloration usually turns out to be gloomy scale, a very common scale insect found on soft maples such as red maple and silver maple. (Silver maples are seen only occasionally in our area.) Red maples under stress are far more likely to fall prey to a gloomy scale infestation. In fact, I see at least some gloomy scale on most of the planted red maples I run across, but don’t recall a specific instance of seeing this insect on trees in the forest or wetlands.

Gloomy scale can be very difficult to control, although home gardeners might consider applications of horticultural oil if the tree is of a reasonable size to spray. But the decision on whether or not to treat is complicated by the fact that so many of these red maples are in unsuitable locations (parking lots being Exhibit A), and have little chance of thriving over the long term. Many of these stressed trees have also picked up mistletoe, which tends to accelerate the downward spiral. Certainly not in every case, but in many cases, the best management call will be replacement with a tougher, more adaptable tree species.

For an excellent update on the gloomy scale situation, visit the website of N.C. State University entomologist Steven Frank at http://ecoipm.com/. Scroll down the main page until you find the May 2 article, “Gloomy Scale on Urban Trees”. If you have trouble accessing the article, let me know and I’ll make sure you get a copy.

In other sobering plant news, cucurbit downy mildew was reported on June 4 in a cucumber field in Wayne County. Cucurbit downy mildew is of concern because of its aggressiveness and ability to significantly reduce yield in a commercial planting. It can also make a mess of your home garden cucurbits.

N.C. State plant pathologists tell us that cucumbers, watermelons and melons are more susceptible to this disease than are squash and pumpkins, but all cucurbits can be at risk if environmental conditions are conducive to disease development.

Lately I seem to be running into quite a number of samples, phone calls and emails regarding red maples with dieback in the canopy and a dark, bumpy material on the branches and twigs.

Red maple (Acer rubrum) is native to Craven County and is quite abundant in and around our wetlands, along streams, and in low-lying areas that tend to stay moist. But red maple doesn’t appear to be particularly adaptable to the non-native stresses and challenges found in parking lots, along streets, and in many home landscapes.

The dark, bumpy discoloration usually turns out to be gloomy scale, a very common scale insect found on soft maples such as red maple and silver maple. (Silver maples are seen only occasionally in our area.) Red maples under stress are far more likely to fall prey to a gloomy scale infestation. In fact, I see at least some gloomy scale on most of the planted red maples I run across, but don’t recall a specific instance of seeing this insect on trees in the forest or wetlands.

Gloomy scale can be very difficult to control, although home gardeners might consider applications of horticultural oil if the tree is of a reasonable size to spray. But the decision on whether or not to treat is complicated by the fact that so many of these red maples are in unsuitable locations (parking lots being Exhibit A), and have little chance of thriving over the long term. Many of these stressed trees have also picked up mistletoe, which tends to accelerate the downward spiral. Certainly not in every case, but in many cases, the best management call will be replacement with a tougher, more adaptable tree species.

For an excellent update on the gloomy scale situation, visit the website of N.C. State University entomologist Steven Frank at http://ecoipm.com/. Scroll down the main page until you find the May 2 article, “Gloomy Scale on Urban Trees”. If you have trouble accessing the article, let me know and I’ll make sure you get a copy.

In other sobering plant news, cucurbit downy mildew was reported on June 4 in a cucumber field in Wayne County. Cucurbit downy mildew is of concern because of its aggressiveness and ability to significantly reduce yield in a commercial planting. It can also make a mess of your home garden cucurbits.

N.C. State plant pathologists tell us that cucumbers, watermelons and melons are more susceptible to this disease than are squash and pumpkins, but all cucurbits can be at risk if environmental conditions are conducive to disease development.

Be suspicious of cucurbit downy mildew if you see angular, yellow to brown lesions, restricted by leaf veins, on the upper surface of leaves. Early in the morning when moisture is higher, you may also note lesions on the leaf undersides covered in a dark downy material. This growth is comprised of masses of pathogen spores called sporangia, which can germinate and infect other leaves and plants. Feel free to drop off samples or e-mail digital images if you suspect cucurbit downy mildew in your garden or field.

Tom Glasgow is the Craven County Extension director. Contact him at tom_glasgow@ncsu.edu.